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Documentation Index

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Subtitle sources are used to add subtitle data to output subtitle tracks. All subtitle sources extend the base SubtitleSource class.

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TextSubtitleSource

Parses subtitle text from a subtitle file format and adds the cues to the output subtitle track.

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Constructor

new TextSubtitleSource(codec: SubtitleCodec)
​
codec
SubtitleCodec
required
The subtitle format/codec used in the text being added. Supported values:
  • 'srt' - SubRip subtitle format
  • 'webvtt' - WebVTT subtitle format
  • 'ass' - Advanced SubStation Alpha format

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Methods

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add

Parses subtitle text according to the specified codec and adds it to the output track. You don’t have to add the entire subtitle file at once - you can provide it in chunks. 
add(text: string): Promise<void>
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text
string
required
The subtitle text to parse and add. Can be the entire subtitle file content or a chunk of it.
​
returns
Promise<void>
Resolves when the output is ready to receive more samples. Await this to respect backpressure.
Example: 
import { TextSubtitleSource } from 'mediabunny';

const subtitleSource = new TextSubtitleSource('srt');

// You can add the entire subtitle file at once
await subtitleSource.add(`1
00:00:00,000 --> 00:00:02,000
Hello, world!

2
00:00:02,500 --> 00:00:05,000
Welcome to Mediabunny.
`);

// Or add it in chunks as you read from a stream
const reader = subtitleFileStream.getReader();
while (true) {
  const { done, value } = await reader.read();
  if (done) break;
  await subtitleSource.add(new TextDecoder().decode(value));
}

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close

Closes the source, preventing future subtitle cues from being added and signaling that no more data will be added to this track. 
close(): void
Calling close() is optional but recommended after adding the last subtitle chunk for improved performance and reduced memory usage.

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Subtitle formats

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SubRip (.srt)

The SubRip format is a simple, widely-supported subtitle format. Each subtitle consists of:
  1. A sequential number
  2. Timing information (start —> end)
  3. The subtitle text
  4. A blank line
1
00:00:00,000 --> 00:00:02,000
First subtitle

2
00:00:02,500 --> 00:00:05,000
Second subtitle

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WebVTT (.vtt)

WebVTT (Web Video Text Tracks) is the native subtitle format for HTML5 video. It supports styling and positioning. 
WEBVTT

00:00:00.000 --> 00:00:02.000
First subtitle

00:00:02.500 --> 00:00:05.000
Second subtitle with <b>formatting</b>

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Advanced SubStation Alpha (.ass)

ASS is an advanced subtitle format that supports complex styling, positioning, and animations. It’s commonly used for anime and fan subtitles. 
[Script Info]
Title: Example

[V4+ Styles]
Format: Name, Fontname, Fontsize, PrimaryColour, SecondaryColour, OutlineColour, BackColour, Bold, Italic, Underline, StrikeOut, ScaleX, ScaleY, Spacing, Angle, BorderStyle, Outline, Shadow, Alignment, MarginL, MarginR, MarginV, Encoding
Style: Default,Arial,20,&H00FFFFFF,&H000000FF,&H00000000,&H00000000,0,0,0,0,100,100,0,0,1,2,0,2,10,10,10,1

[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:00.00,0:00:02.00,Default,,0,0,0,,First subtitle
Dialogue: 0,0:00:02.50,0:00:05.00,Default,,0,0,0,,Second subtitle

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